There is a high turn-over of proteins in all cells, but as far as I know the proteins are broken down into amino acids and then all amino acids can be used again in the next round of protein synthesis. So we shouldn't need much new proteins, since we can reuse what we have (compared to sugar that is broken down into CO2 that is being exhaled).

When we make new cells I understand that we need new amino acids, but there is not a high turn-over of cells in our body, most cells just happily live where they are.

So what accounts for the high need of proteins everyday? My guess is that the reuse of amino acids is not 100 % efficient and that this accounts for the high need of proteins. Is this correct?

We have essential and not essential amino-acids. The essential AA are not produced by our body and need to be found in our food. For not essential AA, some are not enough produced by our cells.Among all these needed AA, some are produced by plant cell and some by animals. Then, we need to eat both plants and animals. Every animals have their own important AA.

Daily protein requirement is to multiply the body weight in kilograms by .8. This is the number of grams of protein that should be the daily minimum. According to this method, a person weighing 150 lbs. should eat 55 grams of protein per day, a 200-pound person should get 74 grams, and a 250-pound person should eat 92 grams.

It is found that although most animals can compensate for not consuming enough carbohydrates by consuming more proteins, eating more carbohydrates does not compensate for not eating enough proteins. There are two reasons for this (as given by JackBean and stephroche). There are certain amino acids (essential amino acids) that cannot be synthesized from other amino acids and need to be consumed. But I think the more important reason is that through processes like gluconeogenesis, amino acids can produce other types of compounds through deamination, but other types of compounds cannot produce amino acids because an amino group is required, which can only be obtained from protein. So you need proteins no matter what. In addition, proteins probably make up the bulk of animal bodies, since their roles are so versatile.